Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A solenoid valve for use in a hazardous environment requiring a surface
temperature of the valve to not exceed a cutoff temperature, the valve
comprising coil configured to physically move an armature using an field
generated by the coil; a thermal cutoff device having a fusing
temperature above the cutoff temperature; and a heating resistor sized
and configured to raise thermal cutoff device's temperature to the fusing
temperature before the surface temperature exceeds the cutoff
temperature. A method of constructing a solenoid valve for use in a
hazardous environment requiring a surface temperature of the valve to not
exceed a cutoff temperature, the method comprising the steps of:
selecting a thermal cutoff device having a fusing temperature above the
cutoff temperature; and selecting and configuring a heating resistor to
raise thermal cutoff device's temperature to the fusing temperature
before the surface temperature exceeds the cutoff temperature.

Claims:

1. A solenoid valve for use in a hazardous environment requiring a
surface temperature of the valve to not exceed a cutoff temperature, the
valve comprising: a coil configured to physically move an armature using
an field generated by the coil; a thermal cutoff device having a fusing
temperature above the cutoff temperature; and a heating resistor sized
and configured to raise a core temperature of the thermal cutoff device
to the fusing temperature before the surface temperature of the valve
exceeds the cutoff temperature.

2. The valve as set forth in claim 1, further including a first lead wire
directly coupled to the coil and a second lead wire coupled to the coil
through the thermal cutoff device and the resistor.

3. The valve as set forth in claim 1, wherein the resistor is wired in
series with the thermal cutoff device.

4. The valve as set forth in claim 1, wherein the resistor is wired in
parallel with the thermal cutoff device.

5. The valve as set forth in claim 1, wherein the resistor is wired in
parallel with a portion of the coil.

6. The valve as set forth in claim 1, wherein the resistor is wired in
parallel with the coil.

7. The valve as set forth in claim 1, wherein the resistor is mounted in
thermal contact with the thermal cutoff device.

8. The valve as set forth in claim 1, wherein the valve is mounted in a
hazardous environment and the resistor is sized and configured to raise
an internal temperature of the valve.

9. A method of constructing a solenoid valve for use in a hazardous
environment requiring a surface temperature of the valve to not exceed a
cutoff temperature, the method comprising the steps of: selecting a
thermal cutoff device having a fusing temperature above the cutoff
temperature; and selecting and configuring a heating resistor to raise a
core temperature of the thermal cutoff device to the fusing temperature
before the surface temperature of the valve exceeds the cutoff
temperature.

10. The method as set forth in claim 9, further including the steps of
coupling a first lead wire directly to the coil and coupling a second
lead wire to the coil through the thermal cutoff device and the resistor.

11. The method as set forth in claim 9, further including the step of
wiring the resistor in series with the thermal cutoff device.

12. The method as set forth in claim 9, further including the step of
wiring the resistor in parallel with the thermal cutoff device.

13. The method as set forth in claim 9, further including the step of
wiring the resistor in parallel with a portion of the coil.

14. The method as set forth in claim 9, further including the step of
wiring the resistor in parallel with the coil.

15. The method as set forth in claim 9, further including the step of
mounting the resistor in thermal contact with the thermal cutoff device.

16. The method as set forth in claim 9, further including the step of
mounting the valve in a hazardous environment and wherein the step of
selecting and configuring the resistor includes selecting and configuring
the resistor to raise an internal temperature of the valve.

[0005] The inventions disclosed and taught herein relate generally to
solenoid valves; and more specifically relate to thermal protection of
solenoid valves operating in hazardous environments.

[0006] 2. Description of the Related Art

[0007] U.S. Pat. No. 3,839,692 discloses "a thermal limiter construction
which can be used to limit one or more electrical circuits and comprises
a thermally responsive device having leads for being interconnected into
such electrical circuit or circuits and a plurality of electrically
operated heaters disposed adjacent the device and each being adapted to
cause the device to open the circuit or circuits when heated by the
respective heater a certain amount."

[0008] U.S. Pat. No. 4,227,169 discloses a "device [that] will open an
electrical circuit in response to either an increase in ambient
temperature or an increase in electrical current. A bracket is provided
to support a radial lead thermal cut-off device. The bracket is of a
general C-shaped configuration and has an extending lead bar that is
crimped into electrical engagement with an input lead, and one radial
lead of the thermal cut-off device is crimped into electrical engagement
with the second input lead. A helical conductive coil has one end welded
or otherwise secured to the C-shaped bracket, and the second lead of the
thermal cut-off device is crimped to the other end of the helical coil
which is positioned over the thermal cut-off device so as to surround it.
Thus, an ambient temperature rise may cause the thermal cut-off device to
open the electrical circuit; or alternately the heat generated by the
I2 R loss in the coil due to excessive electrical current flow may
cause the device to also open."

[0010] U.S. Pat. No. 4,821,010 discloses a "thermal cutoff includes a
housing having a resistive coating bonded thereto, and defining a heater
for heating the thermal cutoff to its firing temperature."

[0011] U.S. Pat. No. 4,968,962 discloses a "thermal cutoff and a heating
resistor are assembled in heat transfer relationship with one another by
a metal clip. The assembly is mounted on a base of dielectric material.
Electric leads on the thermal cutoff and resistor extend through holes in
the base for connection to a printed circuit board."

[0012] U.S. Pat. No. 5,304,974 discloses a "thermal cut-off resistor that
has an elongated thermal cut-off fuse; a wire-shaped resistor that is
tightly coiled around the fuse, said resistor being physically connected
to the fuse so that the fuse and the resistor are in an electrical series
arrangement; and an electrically-insulated heat-resistant casing that
contains the fuse and resistor therein and enables the fuse and the
resistor to be secured and electrically connected to respective
electrical contacts formed on a printed circuit board, the profile of the
casing being approximately the width of the fuse."

[0013] The inventions disclosed and taught herein are directed to an
improved system for thermal protection.

BRIEF SUMMARY OF THE INVENTION

[0014] The present invention relates to a solenoid valve for use in a
hazardous environment requiring a surface temperature of the valve to not
exceed a cutoff temperature, the valve comprising coil configured to
physically move an armature using an field generated by the coil; a
thermal cutoff device having a fusing temperature above the cutoff
temperature; and a heating resistor sized and configured to raise thermal
cutoff device's temperature to the fusing temperature before the surface
temperature of the valve exceeds the cutoff temperature. The present
invention also relates to a method of constructing a solenoid valve for
use in a hazardous environment requiring a surface temperature of the
valve to not exceed a cutoff temperature, the method comprising the steps
of: selecting a thermal cutoff device having a fusing temperature above
the cutoff temperature; and selecting and configuring a heating resistor
to raise thermal cutoff device's temperature to the fusing temperature
before the surface temperature of the valve exceeds the cutoff
temperature.

[0016] The Figures described above and the written description of specific
structures and functions below are not presented to limit the scope of
what Applicants have invented or the scope of the appended claims.
Rather, the Figures and written description are provided to teach any
person skilled in the art to make and use the inventions for which patent
protection is sought. Those skilled in the art will appreciate that not
all features of a commercial embodiment of the inventions are described
or shown for the sake of clarity and understanding. Persons of skill in
this art will also appreciate that the development of an actual
commercial embodiment incorporating aspects of the present inventions
will require numerous implementation-specific decisions to achieve the
developer's ultimate goal for the commercial embodiment. Such
implementation-specific decisions may include, and likely are not limited
to, compliance with system-related, business-related, government-related
and other constraints, which may vary by specific implementation,
location and from time to time. While a developer's efforts might be
complex and time-consuming in an absolute sense, such efforts would be,
nevertheless, a routine undertaking for those of skill in this art having
benefit of this disclosure. It must be understood that the inventions
disclosed and taught herein are susceptible to numerous and various
modifications and alternative forms. Lastly, the use of a singular term,
such as, but not limited to, "a," is not intended as limiting of the
number of items. Also, the use of relational terms, such as, but not
limited to, "top," "bottom," "left," "right," "upper," "lower," "down,"
"up," "side," and the like are used in the written description for
clarity in specific reference to the Figures and are not intended to
limit the scope of the invention or the appended claims.

[0017] Applicants have created a solenoid valve for use in a hazardous
environment requiring a surface temperature of the valve to not exceed a
cutoff temperature, the valve comprising coil configured to physically
move an armature using an field generated by the coil; a thermal cutoff
device having a fusing temperature above the cutoff temperature; and a
heating resistor sized and configured to raise thermal cutoff device's
temperature to the fusing temperature before the surface temperature of
the valve exceeds the cutoff temperature. The present invention also
relates to a method of constructing a solenoid valve for use in a
hazardous environment requiring a surface temperature of the valve to not
exceed a cutoff temperature, the method comprising the steps of:
selecting a thermal cutoff device having a fusing temperature above the
cutoff temperature; and selecting and configuring a heating resistor to
raise thermal cutoff device's temperature to the fusing temperature
before the surface temperature of the valve exceeds the cutoff
temperature.

[0018] In applications of solenoid valves in hazardous environments it
critical that the temperature of the surface of a coil of the valve never
exceeds certain predetermined limits based on the type of potentially
explosive atmospheres that may be present. One method of insuring that
this will not occur is by the inclusion of a thermal cut off (TCO) device
on the winding of the coil. If an abnormal condition occurs, such as a
solenoid valve becoming stuck in the closed position and when power is
applied the solenoid was unable to move it's armature to the full open
position, power consumed by the coil would increase to a level which
would make it's surface temperature exceed the safe limits of the
environment. This scenario is avoided by the presence of the TCO, which
will open the electrical circuit when the coil meets or exceeds its
cutoff temperature.

[0019] There are a number of TCO technologies available to accomplish
this, but the most reliable on for this type of a critical application is
the eutectic type TCO. These devices are typically composed of a ceramic
tube filled with an eutectic alloy with electrical connections extending
from each end. The lead wires are secured in the tube with a high
temperature epoxy compound.

[0020] The fusing temperatures of these devices are accurate since they
are based on the eutectic melting properties of the alloy chosen. Since
there are a finite number of eutectic alloy combinations that melt at
certain temperatures the operating temperatures are limited to what we
find in nature. Designs must be tailored to the available temperatures.
However, there are finite combinations, and thus there are finite fusing
temperatures. If a different fusing temperature is needed these prior art
devices do not provide a solution.

[0021] One purpose of the present invention is to be able to adjust the
operating point of a given TCO device by electrically coupling it to a
heating resistor that is in thermal contact with the TCO device with a
fusing temperature that is greater than the desired cutoff temperature
for the coil. The heating resistor is sized so that, in an abnormal
condition of operation of the solenoid valve, the power this resistor
consumes will provide the additional temperature rise in the TCO device
to allow it to reach the higher fusing temperature, while the coil
winding and subsequently the surface temperature of the coil is kept at a
value that is safe for the environment in which it is operating.

[0022]FIG. 1 is an illustration of one particular embodiment of just such
a system 10. As shown, one of two lead wires 12 is directly connected to
one of two terminals 14 of a coil 16 for a solenoid valve. The other lead
wire 18 is connected to a thermal cut off (TCO) device 20. The TCO device
20 is deliberately chosen to create an open circuit at a fusing
temperature that is greater than the desired cutoff temperature for the
hazardous environment in which the solenoid valve will operate. This, of
course, goes directly against the current teaching in the relevant arts.

[0023] In order to protect the solenoid valve, and surrounding equipment
in the hazardous environment, and ensure that the TCO will trip when, or
before, the surface temperature of the solenoid valve reaches the desired
cutoff temperature for the hazardous environment in which the solenoid
valve will operate, a heating resistor 22 is thermally coupled to the TCO
20. As current flows through the coil 16, the TCO's 20 temperature rises.
As current flows through the resistor 22, the TCO's 20 temperature rises.
The temperature of the coil 16 and the resistor 22 thereby cooperate to
raise the TCO's 20 temperature above that of the coil 16 alone. Once the
temperature of the TCO 20 meets or exceeds its fusing temperature, the
TCO 20 trips thereby creating an open circuit and preventing the surface
temperature of the solenoid valve from exceeding the desired cutoff
temperature for the hazardous environment.

[0024] In other words, the resistor 22 is preferably sized to transfer
sufficient heat to the TCO 20, whenever an abnormal condition exists.
More specifically, the resistor 22 is preferably sized such that a fault
current will generate sufficient heat to quickly raise the temperature of
the TCO 20 to its fusing temperature, and thereby trip the TCO 20, before
the surface temperature of the solenoid valve exceeds the desired cutoff
temperature. Alternatively or additionally, the resistor 22 may be sized
such that any abnormal condition, such as when a solenoid valve becomes
stuck in the closed or open, producing an abnormal current through the
resistor 22 will generate sufficient heat to raise the temperature of the
TCO 20 to its fusing temperature, over time, and thereby trip the TCO 20,
before the surface temperature of the solenoid valve exceeds the desired
cutoff temperature.

[0025] As shown, the TCO 20 and the resistor 22 may be wired in series
between one of the leads 18 and one of the terminals 24 of the coil 16.
However, in other applications, the TCO 20 and the resistor 22 may be
wired independently and/or wired in parallel.

[0026] The resistor 22 and TCO 20 may be potted within the solenoid valve
assembly to prevent the hazardous environment from being exposed to the
temperature of the resistor 22 and/or TCO 20. This may allow the solenoid
valve to meet any required certifications for the hazardous environment.
For example, the present invention allows the solenoid valve to be
reliably disabled at a cutoff temperature well below the fusing
temperature of the TCO 20. This, in turn, allows virtually any cutoff
temperature specification to be met, depending upon the
size/rating/resistance/value of the heating resistor, independently of
the available TCO ratings. In other words, one need not have a TCO rated
at the exact cutoff temperature specification needed. Rather, one can use
a readily available TCO, with a rating higher than the cutoff temperature
specification, and then size the resistor to raise the TCO's temperature
before the coil exceeds the cutoff temperature specification.

[0027] Other and further embodiments utilizing one or more aspects of the
inventions described above can be devised without departing from the
spirit of Applicant's invention. Further, the various methods and
embodiments of the present invention can be included in combination with
each other to produce variations of the disclosed methods and
embodiments. Discussion of singular elements can include plural elements
and vice-versa.

[0028] The order of steps can occur in a variety of sequences unless
otherwise specifically limited. The various steps described herein can be
combined with other steps, interlineated with the stated steps, and/or
split into multiple steps. Similarly, elements have been described
functionally and can be embodied as separate components or can be
combined into components having multiple functions.

[0029] The inventions have been described in the context of preferred and
other embodiments and not every embodiment of the invention has been
described. Obvious modifications and alterations to the described
embodiments are available to those of ordinary skill in the art. The
disclosed and undisclosed embodiments are not intended to limit or
restrict the scope or applicability of the invention conceived of by the
Applicants, but rather, in conformity with the patent laws, Applicants
intend to fully protect all such modifications and improvements that come
within the scope or range of equivalent of the following claims.